There are several types of archery bows and crossbows, that have been used over the years. Vertical bows and crossbows will be herein collectively referred to as “bows”. Traditional vertical bows include long bows and recurves. These are typically made of only wood and have no mechanical parts. Compound bows, on the other hand, have eccentric wheels or camps that rotate as the bowstring is pulled to a shooting position. These bows typically have one or more cams or wheels that are attached to flexible limbs or the frame of the bow by an axle or pivot pin. A cam, when embodied within a bow, provides mechanical advantage for the shooter. When the bowstring is drawn, the flexible limbs will be stressed and store potential energy that will later be used to launch an arrow. The advantage of a compound bow over traditional bows is that when at full draw, less force is required to hold the bow than is required to draw it. This is called “let off” and typically varies from 50% to 85% of the peak draw force. Traditional bows require a steady increase in force to draw the bow to a full draw position. The advantage of “let off” is that the archer can remain at full draw for a long period of time and yet be able to control the bow.
The velocity of a bow is important because the faster the flight of the arrow, the flatter its trajectory and the less important is the estimation of range. Furthermore, arrows that possess high velocities will penetrate the target better. For hunters, this means the arrow is more likely to pass completely or substantially completely through the animal.
There are several ways for increasing the shooting velocity of a bow and arrow combination. The limitations are that most archers cannot draw more than 65-70 pounds, and youth and women typically cannot draw more than 45-50 pounds. Draw weight is the easiest method of increasing arrow speed, but is the most difficult on the shooter. Another approach is to increase the power stroke length of the bow. Power stroke is the distance of the draw from the at rest or braced position and the full draw position. This is approximately the draw length of the individual bow minus the brace height which is a perpendicular distance from the at rest position of the string to the riser. This is also easily changed. However, archers have size limitations that make it difficult to shoot a bow having a relatively large draw length. Also, the shorter the brace height, the more difficult it is to shoot the bow. Typical power strokes are limited to about 20 inches. Another way to increase bow velocity is to make the bow more efficient. This can be expensive and usually does not yield substantial benefits.
Yet another approach is to utilize lighter arrows. This is also an easy way of increasing arrow speed. The potential energy stored in the bow is transferred to kinetic energy of the arrow. The lighter the arrow, the faster it will travel when shot from the same bow. However, there are safety minimums on arrow weight that are based upon the shooting force of the bow. There is a lower limit to the arrow weight based upon the shooting force. If the bow is shooting arrows that are too light, much of the potential energy of the bow is absorbed by the bow as vibrations and stress, as opposed to being transferred to the arrow.